Flash arrester for pulsed arc discharge tubes



April 7, 1970 1 cLH. CHURCH 3,505,555

' FLASHARRESTER FOR VPULSED ARC DISCHARGETUBES Filed Feb. 19, 1968 FIG. 2

Charles H. Church,

w TOR.

United States Patent US. Cl. 313219 6 Claims ABSTRACT OF THE DISCLOSURE A flash. arrester for a pulsed arc discharge tube having the electrodes thereof disposed coaxially with the tube. The: tube may be of quartz; or ceramic material and the electrodes are secured to the tube by adhesives such as epoxies or silicones. A conductive device is installed between the electrodes and the adhesive to prevent radiation from damaging the adhesive bond.

BACKGROUND OF THE INVENTION Pulsed arc discharge tubes are currently being assembled with the electrodes disposed coaxially with the tube. For example, in a coaxial ruby laser system, a ruby rod is concentrically mounted in a "tube support structure which may be of quartz or ceramic material and the electrodes are coaxially disposed around the tube and assembled thereto by adhesives such as epoxies and silicones. One of the physical properties'of these adhesive materials that is highly desirablefor this application is flexibility. However, the adhesive is subjected to damages, such as volatilization, by radiation during periods when the tube is active. Radiation damage to the adhesive seal has been minimized in the past by using reasonably great distances of separation ofthe adhesive and the arc region of the electrodes, which not only involves more bulkiness in the tube structure but requires the use of more material in construction of the tube.

SUMMARY OF THE INVENTION An object of this invention is to provide a means for protecting the adhesives in an arc discharge tube from damage incurred directly or indirectly from the are, thereby prolonging the tube life.

The insertion of a flash arrester between the electrode arc region and the adhesive joint between the electrode and the ihsulating ceramic or quartz prevents radiation from impinging upon the adhesive; Not only is tube life prolonged but the tube is more reliable and shorter coaxial tubes can be produced without sacrificing efliciency or life of the tube. The material used in construction of the tube is also reduced, thereby reducing the cost and size of the tube.

BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 is an end view of a coaxial tube;

FIGURE 2 is a section taken along the lines 22 of the coaxial tube of FIGURE 1 showing the relative location of the flash arrester with fespect to an adhesive joint; and

FIGURE 3 is a detail of a linear tube showing the relative location of the flash arrester with respect to the adhesive.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings wherein like reference characters designate like or corresponding parts in all views, FIGURE 1 discloses a preferred embodiment of "Ice the invention. An electrode structure 10 is fixedly attached by an adhesive 14 to a ceramic tube 12. In an arc discharge tube under operating conditions the e ectrode, adhesive, and ceramic are exposed to high temperatures, which result in an expansion of the three. When the tube is returned to a passive condition, the gradually cooling components slowly contract. This bonding material, electrode structure, and ceramic tube must have similar coeflicients of expansion such that a greater expansion in one or a faster reduction (while cooling) in another will not produce more stress than the combined structure can withstand. The adhesive bonding material 14 is an epoxy or silicone, desirable for this type of application because of its flexibility, which allows for changing dimensions of electrode 10 and ceramic 12, due to temperature difierentials, without weakening the structure. However, under operating conditions, heat radiation from the electrode arc damages the adhesive 14 resulting often in tube breakdown early in the life of the tube.

A coiled metallic flash arrester 16 is disclosed in FIG- URE 2.'Flash arrester 16 is placed between the adhesive 14 and the arc region of electrode structure 10. To maintain the elasticity of the joint, which is necesary to give proper shock and stress resistance, the flash arrester should be elastic also. Elasticity is maintained in flash arrester 16 by forming it of overlapping coils of a fine metallie spring, which is coiled about the ceramic 12 and fits loosely in a groove 18 in the electrode structure 10. The overlapped coils of spring 16 prevent radiation from impinging upon adhesive 14, and are elastic enough to prevent restriction of the motion of ceramic 12.

FIGURE 3 discloses another embodiment of the invention wherein the electrode structure 10 is located within the ceramic tube 12. Flash arrester 16 is located between the adheive 14 and an arc region 20 of electrode structure 10. The flash arrester is coiled around electrode structure 10 adjacent to the ceramic tube 12 and is insulated from the actual conducting electrode in arc region 20. The size of electrode 10, as used in either figure, may be reduced since a great distance is no longer required between the arc region and the adhesive bond 14. This can also result in a reduction in the length of ceramic 12 required for mounting electrode structures.

In operation of the tube, radiant energy in the form of heat is generated when the tube is arcing. The heat radiation, which normally tends to move away from the arc region through ceramic 12, attacks adhesive 14 and gradually weakens the structure therethrough as mentioned previously. Flash arrester 16, lying between the arc region and adhesive 14, draws this radiant energy thereto, thereby reducing the heat build-up near adhesive 14. The heat build-up on flash arrester 16 causes arrester 16 to become the effective heat sink of the tube, reducing the heat that is applied directly to adhesive 14 and more rapidly cooling the tube.

The coiled springs of flash arrester 16 may be separated from the electrode structure in any convenient manner. Typically, as shown in FIGURES 2 and 3, a voild separates the two elements. Compression of spring 16 in FIG- URE 3 causes the spring to attempt to restore and thereby force itself outwardly against the ceramic. Similarly, in FIGURE 2, if spring 16 is placed under slight tension when inserted, the spring will try to move inward against the ceramic. These restoring forces hold the springs in place against the ceramic.

I claim:

1. An arc discharge tube flash arrester comprising: a ceramic tube having an electrode structure coaxially aligned therewith for providing an arc discharge, adhesive means bonding said electrode structure to said tube,

and a resilient metallic flash arrester means disposed intermediate said electrode structure and said tube for preventing radiation from impinging upon said bonding means.

2. The flash arrester as set forth in claim 1 wherein said flash arrester means is a flexible strip of metal insulated from said electrode structure.

3. The flash arrester as set forth in claim 1 wherein said flash arrester means is overlapping coils of a fine metallic spring coiled about the ceramic and enclosed 10 5. The flash arrester as set forth in claim 1 wherein 15 said flash arrester means is overlapping coils of a fine metallic spring coiled about the electrode structure and 5 hesive bond and the electrode arc region.

References Cited UNITED STATES PATENTS 1,144,028 6/1915 Creighton 3l3219 X RAYMOND F. HOSSFELD, Primary Examiner US. Cl. X.R. 

